Automotive camera modules are exposed to temperatures varying over a large range, and are required to have excellent imaging performance over the whole temperature range occurring in use.
In many fixed-focus automotive camera modules, a major challenge is to retain the focus over the temperature envelope T. For low f/# lenses, the distance between the image and the sensor must be controlled at a scale of micrometers.
Temperature differences lead to a respective change of the dimensions of the housing of the camera module. For instance, the height of the housing increases due to thermal expansion with an increase of the housing temperature. Accordingly, a distance between the lens assembly, usually attached to a front end of the housing, and the image sensor, usually arranged at a back end of the housing, increases with a temperature increase, resulting in the sensor moving out of the image plane of the lens assembly. Consequently, at high or very low temperatures the image sensor may not detect an image as clear as at moderate temperatures.
U.S. Pat. No. 7,595,943 B2 discloses a camera module which includes a plurality of lenses, including a lens barrel holding the plurality of lenses, a housing part holding the lens barrel and an image sensor, and two spaced thermally deformable members. The thermally deformable members are arranged in a radial plane of the lens barrel. In order to connect the housing part and the lens barrel, each of the thermally deformable members has one end attached to the peripheral side wall of the lens barrel and an opposite end attached to an inner side wall of the housing part. Each of the thermally deformable members has a multilayer sheet configuration with a first sheet arranged above a second sheet. Thus, the first sheet is disposed at an object side of the lenses and the second sheet is disposed at an image side of the lenses. A thermal expansion coefficient of the second sheet is larger than the thermal expansion coefficient of the first sheet. With the temperature of the thermally deformable member increasing from the first temperature to the second temperature, the second sheet progressively bends toward the first sheet and drives the lens barrel upwards along an optical axis. Such a camera module has many components and is quite complex.
DE 10 2008 047 277 Al discloses a generic camera module where a compensating tube is provided between a lens carrier and a lens barrel. The compensating body may have an inner thread into which the lens barrel may be screwed. Due to the relatively long axial length of the lens barrel, the length of the compensating tube which can move freely is very small and a substantial compensation can be hardly achieved.
DE 102 61 973 Al discloses a camera module where the lens is indirectly held by a housing tube via a frusto-conical lens holding element which has a significantly smaller thermal expansion coefficient than the housing tube.
The object of the present invention is to provide camera module having a simple mechanism to keep the image sensor at an image plane of the lens assembly.
The object of the invention is achieved by a camera module and a method of mounting a camera module as described herein.